Elvis Costello

Maybe it's true: The longer you stick around rock 'n' roll, the more likely you'll end up at the place where it all started.

There's no doubt that Elvis Costello launched his musical trip years ago with a firm grasp on rock's roots, his biting British pop molded with a nod to the throwback sound, even look, of the 1950s.

But as Costello arrived at last fall's The Delivery Man, his latest creative detour, in a career that's become defined by them, he found himself quite literally at the crossroads — in the heart of Clarksdale, Miss. Nearly three decades after landing on the budding punk and new wave scene with a blast of whip-smart pub rock, Costello had made his way to the ancient cradle of Delta blues.

The Clarksdale Sessions, a seven-song set available on vinyl and on a newly beefed-up edition of Delivery Man, showcases the artist's head-first plunge into the American backwaters where the proteins and polymers of rock came to life.

Costello's Southern sojourn was "a chance thing," he says — much like the other stylistic twists and turns in a recent period that has seen him embrace jazz, score an Italian symphony and marry Canadian trad-pop vocalist Diana Krall.

"It's been a musical instinct every time, not what was right commercially or anything like that," says Costello, whose country dabbling stretches back to an unreleased 1977 duet with George Jones. "When I was on the road in 2002, we happened to play the tail end of the tour in the South. I had this feeling that it was the right place to keep working.

"I needed something the band could thrive on musically. We needed songs that could hold their own in the set against these songs that have been around for 25 years."

The seeds of his new summer tour were planted last fall. Performing at a tiny Memphis club with his band the Imposters — a set filmed for the new ''Live in Memphis DVD — Costello was joined by the velvet-voiced Emmylou Harris for a five-song stretch.

"The grace she brings to the stage is just something else," he says.

Costello goes out of his way to clear up misconceptions about the new tour with Harris, which has been mislabeled in some quarters as a double-headlining affair. In fact, "she's actually in the band," Costello says — "the featured singer in a portion of the show. Her numbers will be inside our set. Don't get there late, because you'll miss something."

The tight, two-part harmony isn't the only new element in Costello's set. The show, which features Costello standards among the new rootsy material, benefits from the versatility of the Imposters, a crack band with guitarist-vocalist Davey Faragher joining longtime players Steve Nieve (keyboard) and Pete Thomas (drums), and guitarist Larry Campbell, who logged seven years in Bob Dylan's touring band, will take the stage for a handful of numbers.

"I've got a pretty great band, and I know they can surprise me — suddenly the picture emerging around me onstage might nudge me to sing a different way" Costello says. "It's a different kind of band for me. very much rooted in the relationship between the bass and drums. I've been drawn more toward that kind of sound, coincidentally now that I've got it at my disposal."

It's no secret that Costello is one of rock's bona fide intellectuals, an artist whose knack for connecting cultural dots and analyzing his own work has long been part of his stock in trade. Though his notorious cynicism is tempered as he approaches his 50th birthday next month, he says he remains constantly plagued by self-doubt, saddled with "dark thoughts about every single piece of work I've made."

And while he recognizes the danger of letting his brain get in the way of himself — the battle between his cerebral side and his musical instinct — he figures his own limitations have kept him from straying too far from rock authenticity.

"I'm fortunate in that I'm not that schooled as a guitar player," he says. "I just play my own way. So there's kind of an idiot, primitive side to what I do, all the time."